1. Field of the Invention
This application is directed to quaternary ammonium salts of mercaptothiadiazoles and related heterocyclic derivatives as multifunctional antioxidant/antiwear additives for lubricants and fuels and to compositions containing same.
Lubricants, such as lubricating oils and greases, are subject to oxidative deterioration at elevated temperatures or upon prolonged exposure to the elements. Such deterioration is evidenced, in many instances, by an increase in acidity and in viscosity, and when the deterioration is severe enough, it can cause metal parts to corrode. Additionally, severe oxidation leads to a loss of lubrication properties, and in especially severe cases this may cause complete breakdown of the device being lubricated. Many additives have been tried, however, many of them are only marginally effective except at high concentrations. Improved antioxidants are clearly needed.
Antioxidants or oxidation inhibitors are used to minimize the effect of oil deterioration that occur when hot oil is contacted with air. The degree and rate of oxidation will depend on temperature, air and oil flow rates and, of particular importance, on the presence of metals that may catalytically promote oxidation. Antioxidants generally function by prevention of peroxide chain reaction and/or metal catalyst deactivation. They prevent the formation of acid sludges, darkening of the oil and increases in viscosity due to the formation of polymeric materials.
Additionally, lubricants are under heavy stress that can affect their extreme pressure/antiwear and load carrying ability particularly between steel on steel moving surfaces.
2. Description of Related Art
The use of thiadiazole derivatives, such as 2,5-dimercapto-1,2,4-thiadiazole, for their antioxidant, anticorrosion and metal passivating properties when incorporated into oleaginous compositions is well known as disclosed in U.S. Pat. No. 4,661,273, U.S. Pat. No. 4,678,592 and U.S. Pat. No. 4,584,114. U.S. Pat. No. 4,410,703 discloses the use of thiadiazoles substituted with certain other moieties such as the organophosphorous moiety.
It is an object of this invention to provide lubricant compositions having enhanced oxidative stability, reduced wear, increased load carrying/EP capabilities and improved lubricity. Additional benefits can include antifatigue, cleanliness, detergency, dispersal, corrosion inhibiting, antirust antispilling, friction reducing, low-temperature improving and combustion improving properties. It also is an object of this invention to provide improved fuel compositions.
Traditional quaternary ammonium salts consist of a) a tetra-alkylated amine cation, and b) an inorganic counter-anion such as halide, perchlorate and hexaflurophosphate, etc. These quaternary salts have been widely used in industrial and household applications as cleaning detergents. Little or no attention has been paid to them for use as lubricant additives due to their ionic nature which can make them incompatible with and insoluble in organic lubricating oils. However, these difficulties have been addressed by our recent finding that selected quaternary ammonium salts can be converted into organic quaternary ammonium salts composed of a (alkyl)x(aryl)yN.sup.+, where x+y=4, cation and an organic counteranion such as anionic dimercaptothiadiazole as exemplified in this patent. These organic quaternary ammonium salts are generally soluble in both mineral base stocks and ester-based synthetic lubricants and exhibit surprisingly good antioxidant and antiwear activities.